i965/fs: Also do the gen4 SEND dependency workaround against other SENDs.

i965/fs: Also do the gen4 SEND dependency workaround against other SENDs.

We were handling the the dependency workaround for the first written reg
of a send preceding the one we're fixing up, but didn't consider the other
regs.  Thus if you had two sampler calls that got allocated to the same
set of regs, one might, rarely, ovewrite the other.  This was occurring in
XBMC's GLSL shaders.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44567
NOTE: This is a candidate for the stable branches.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>